Elongated aperture electron gun structure for flat cathode-ray tube

ABSTRACT

An electron gun for a flat cathode-ray tube wherein the control electrode and the screen electrode of the gun each have an elliptical aperture therein, and a flat cathode-ray tube employing such a gun. The major axes of the two elliptical apertures lie in a common plane which is oriented with respect to the faceplate of the tube so that an electron beam emitted by the cathode of the gun produces a substantially circular spot on said faceplate.

United States Patent I Filed Robert C. Jones Elkins Park, Pa. 772,232

Oct. 31, 1968 May 18, 1971 Philco-Ford Corporation Philadelphia, Pa.

inventor Appl. No.

Patented Assignee ELONGATED APERTURE ELECTRON GUN STRUCTURE FOR FLATCATHODE-RAY TUBE 9 Claim, 6 Drawing Figs.

U.s.c| 313/86, 313/299 Int.Cl H0lj 1/46, H0lj29/46 FieldofSearch313/86.85

[56] References Cited UNITED STATES PATENTS 2,836,752 5/1958 Berthold 3l 3/86X 2,884,559 4/1959 Cooper. Jr. et a]. 3 l3/86X PrimaryExaminer-Roy Lake Assistant Examiner-V. Lafranchi Attorney-HerbertEpstein ABSTRACT: An electron gun for a flat cathode-ray tube whereinthe control electrode and the screen electrode of the gun each have anelliptical aperture therein, and a flat cathode-ray tube employing sucha gun. The major axes of the two elliptical apertures lie in a commonplane which is oriented with respect to the faceplate of the tube sothat an electron beam emitted by the cathode of the gun produces asubstantially circular spot on said faceplate.

Patented May 18, 1971 3,579,010

2 Sheets-Sheet l INVENTOR. 05597 (3 JO/Vff fMWQ 3%..

Patented May 18, 1971 3,579,010

2 Sheets-Sheet 2 .ra J4 f6 f6 37 45 J6 46 INVENTOR.

BY QK M ATTORNEY ELONGATED APER'IURE ELECTRON GUN STRUCTURE FORCATHODE-RAYTUBE Cathode-ray tubes in which the viewing faceplate issubstantially flat and thebeam deflection system of tube is positionedso that a line from the center of deflection of the tube to the centerof the faceplate of the tube makes an acute angle with the faceplate(hereinafter referredto as flat cathode-ray tubes" or flat tubes") areadvantageous because they have flat viewing screens and occupy lessspacein a direction perpendicular to the faceplate than do cathode-ray tubesin which the line from the center of deflection to the center of thefaceplate is perpendicular to the faceplate. The latter tubes arereferred to hereinafter as conventional tubes." I-Iowever, flat tubeshave beam-focusing problems not found in conventional cathode-ray tubes.Because of the aforedescribed angular relationship iii 'a-' flat tube,an electron beam of circular cross section produces; wherever itimpinges on the faceplate, an elliptical spot elongated in substantiallya single direction. By contrast, in a conventional cathode-ray tube, anelectron beam of circular cross section produces a circular spot oflight when perpendicular to the faceplate of the tube and, when notperpendicular, produces a spot elongated in a direction which changes asthe point of impingement of the beam is changed.

In both kinds of tubes it is desirable that a sharply focused circularspot of light be produced wherever the beam impinges the viewing screen.To this end, focus correction systems for altering the cross-sectionalshape of the beam have been proposed for conventional tubes. However,since the way in which spots elongate in flat tubes is considerablydifferent from the way in which spots elongatein conventional tubes, thefocus correction systems applicable to conventional tubes are useless inflat tubes. 7

An object of the presentinvention is to provide a cathoderay tube shortin a direction perpendicular to the viewing screen.

Another objectis to provide a flat cathode-ray tube with an improvedelectron gur for providing defocusing correction. A

A further object is to provide an electron gun the beam of whichproduces a substantially circular spot wherever it impinges thefaceplate of a flat cathode-ray tube. y

In general, these and other objects of the present invention areachieved in a flat tubeby use therein of an electron gun the controlelectrode and the screen electrode of which have respective elongatedapertures therein. I

Preferably, the apertures in the controlelectrode'and the screenelectrode are elliptical with coplanar major axes. Such electrodessupply an electron beam of elliptic cross section to the main focusinglens of the electron gun. The major axes of the elliptical apertures areoriented so that the plane defined by said major-axes intersects thescreen'of the tube along a line which extends in'a direction transverseto the direction of elongation of the spots which would be produced on,the screen if a beam of circular cross section were incident thereon.Preferablythe aforementioned plane intersects the screen of the tubealong a line which is perpendicular to the aforementioned direction ofelongation. Due to the orientation of the elliptical apertures and theacute angle that exists in a flat cathode-ray tube between the lineextending from the center of deflection of the tubeto the center of thefaceplate of the tube, theregion of the faceplate impinged by theelliptically shaped beam is substantially circular, and therefore a highresolution image can be formed by the beam on the faceplate of the tube.a 7

Other objects and features of the invention will become apparent in thecourse of the following detailed description of the accompanyingdrawings, of which: e

FIG. I shows a perspective view of a flat cathode-ray tube incorporatingan electron gun structure according to the invention; v j

FIG. 2 is asectional view of the tube'shown in FIG. 1 taken along theline 2-2and viewed in the direction indicated by the arrows; 7

FIG. 3 is a perspective view, partlyin section, of

the electron gun of the present invention;

FIG. 4 is a side elevation in section of the electron gun of FIG. 3; andv i j FIGS. 5 and 6 illustrate respectively the shape of spots producedon a section of faceplate of a flat cathode-ray tube comprising anelectron gun which produces a beam of circular cross section and theshape of spots produced on a section of the faceplate of a flatcathode-ray tube comprising the electrode gun structure of FIGS. 3 and4.

' FIGS. I and 2 show a flat cathode-ray tube in accordance r faceplateforms an acute angleG withfaceplate 25. An

electron gun 26 in neck section 22 is adapted to project an electronbeam onto a target 28 which in the embodiment of the invention shown isa luminescent screen on faceplate 25. Screen 28 may comprise a layer 30of phosphor material with a film 32 of aluminum thereon. Alternatively,screen 28 may be any other type of electron-beam-responsive screen suchas the type of screen used in a storage tube. Beam deflection apparatus34 is disposed between the electron gun 26 and the viewing section 12for deflecting the electron beam across the screen 28. Beam deflectionapparatus 34 may comprise a first pair of electrostatic plates and asecond pair of electrostatic plates oriented perpendicular to the firstpair of plates. Alter natively, apparatus 34 may comprise a first pairof coils whose axes extend in one direction and a second pair of coilswhose axes are perpendicular to the axes of the first pair of coils.Where electrostatic plates are used deflection of the electron beam isachieved by applying appropriate potentials to the plates. Where coilsare used deflection of the electron beam is achieved by passingappropriate currents through the coils. While the r deflection apparatus34 is depicted as located within envelope 10, it is to be understoodthat deflection apparatus 34 may be located outside envelope [0.

Neck 22 is closed at its free end with a stern structure 35 whichincludes a plurality of lead-in conductors 36 for applying suitablevoltages to the electrodes of the electron gun.

FIGS, 3 and 4 show the principal elements of electron gun 26 of FIG. I.Gun 26 comprises a tubular control electrode cup 38, a tubular screenelectrode cup 40, and a focusing-accelerating lens comprising tubularelectrodes 42 and 44. A tubular thermionic cathode 46 (FIG. 4) ismounted in a centrally apertured insulating disc 48 which in turn isfixed within the control electrode cup 38. Cathode 46'is closed at oneend, and is coated on the other end with an electron-emissive materialto provide a circular electron-emissive surface 47. To heat cathode 46 aheater of conventional form (not shown) may be provided therefor. Theelectrodes of the electron gun are rnou nted in coaxial spacedrelationship along a pair of insulating rods 52 and 54 by mounting studs56 which are fixed to the electrodes and embedded in the insulating rods52 and .54. Typically electrodes 38, 40, 42 and 44 are made of 305"stainless steel, and rods 52 and 54 are made of glass.

In operation both electrode 42 and electrode 44 are supplied withpotentials hig hly positive with respect to the potential of cathode46.The potential supplied to electrode 44 is higher than that supplied toelectrode 42. Electrode 42 and 44 accelerate the electron beam passingthrough screen electrode 40 and produce a focusing field which causesthe electron 'bea rn passing through screen electrode 40 to converge toa by passage through aperture 41. To this end, aperture 41 preferably ismade slightly larger than aperture 39. Preferably the ratio of thelength of the major axis to the length of the minor axis, hereinafterreferred to as axial ratio, of each apertures 39 and 41 is between about1.3 and about 2.5. The optimum axial ratio depends on the value of theimpact angle 2 (F162). As the value of D is decreased, the axial ratioof apertures 39 and 41 is increased.

The major axes of apertures 39 and 41 are oriented so that the planedefined thereby intersects screen 28 along a line transverse to thedirection in which the spot of light produced on screen 28 by theelectron beam from gun 26 would be elongated if gun 26 produced anelectron beam of circular cross section instead of a beam of ellipticalcross section, or if a beam of circular cross section were projectedalong the line extending from the center of deflection of the tube tothe center of the faceplate of the screen. Preferably, said planeintersects screen 28 along a line which is perpendicular to theaforementioned direction of elongation.

FIG. 5 illustrates the shape of spots 58 that are produced on screen 28when the electron beam 60 incident thereon is of circular cross section.Spots 58 are elongated in the direction of dashed line 62. Suchelongated spots are undesirable because they cover unnecessarily largeareas of the screen and hence degrade the image resolution obtainablewith the tube.

FIG. 6 illustrates the results realized by utilizing the electron gun ofthe present invention positioned as described hereinbefore. inaccordance with the invention, elliptical beam 64 produced by theelectron gun of FIGS. 3 and 4 is oriented so that substantially circularspots 66 are produced on screen 28.

In the embodiment of the invention shown in FIGS. 1 and 2, that is, withthe neck section 22 of tube 10 attached opposite a vertical panel 14 ofviewing section 12, the common plane containing the major axes ofapertures 39 and 41 is a vertical plane. However, neck section 22 oftube 10 alternatively may be attached opposite a horizontal panel ofviewing section 12, e.g. where panel 18 not located. In such a case themajor axis of each aperture is horizontal and the major axes of bothapertures are coplanar.

in the embodiment of the invention wherein the structure of the electrongun is that shown in FIGS. 3 and 4, the various electrodes typically mayhave the following dimensions and spacings:

Outside diameter of all electrodes, in 395 Inside diameters of allelectrodes, in- 375 Axes of elliptical apertures:

Electrode 38 Major axis, in .036 Minor axis, in 018 Electrode 40 Majoraxis, in 044 Minor axis, in 022 Spacing between cathode 46 and electrode38, in 006 Spacing between electrodes 38 and 40, in 007 Spacing betweenelectrodes 40 and 42, in. 040 Spacing between electrodes 42 and 44, in.100

Length of electrode 38, in Length of electrode 40, in Length ofelectrode 42, in Length of electrode 44, in Distance from center ofdeflection 23 to the Dizsfitalnce from cathode emitting surface 47 tothe center of so 11 Suitable D.C. voltages for operating such a gun areas follows:

Electrode 38 65 v. below cathode potential. Electrode 40... 400 v. abovecathode potential. Electrode 42. 400 to 800 volts above cathodepotential. Electrode 44 kv. above cathode potential.

rfiicamiic'faig as? such a gun are as follows:

production of an electron beam of elliptical cross section by theelectron gun may be facilitated by providing one or more of theelectrodes thereof with an elliptical internal cross section and/or byusing a cathode that emits an electron beam of elliptical cross section.The major axis of each such electrode and such electron beam should liein the plane defined by the major axes of apertures 39 and 41.

Moreover, where circularity of the spots formed on the faceplate of thetube is not essential, elongated apertures other than ellipticalapertures may be provided in electrodes 38 and 40. For example, theapertures in electrodes 38 and 40 can be rectangular with the long sidesof one rectangular aperture parallel to the long sides of the otherrectangular aperture. I

Furthermore a three electrode einzel lens can be submitted for thefocusing-accelerating lens comprising electrodes 42 and 44. An einzellens comprises a pair of electrodes each maintained at a potentialhighly positive with respect to the cathode and a third electrodeintermediate the pair of electrodes and at a potential intermediate thecathode potential and the potential of the pair of electrodes.Accordingly, I desire the scope of my invention to be limited only bythe appended claims.

lclaim:

1. in a cathode-ray tube comprising an electron-beamresponsive screen,means for projecting a beam of electrons thereagainst, and electron beamaccelerating-focusing apparatus, said means comprising anelectron-emissive cathode, a control electrode and a screen electrode,said tube having a center of deflection for said beam, saidbeam-responsive screen being oriented at an angle acute with respect toa line connecting said deflection center and the center of said screen,the improvement comprising an elliptical aperture in said controlelectrode and an elliptical aperture in said screen electrode, the majoraxes of both said apertures lying in a common plane.

2. The tube of claim 1 wherein said apertures are coaxial.

3. The tube of claim 2 wherein said apertures are oriented so that saidcommon plane intersects said screen in a direction transverse to thedirection in which a spot would be elongated if produced on said screenby a beam of circular cross section projected along said line.

4. The tube of claim 3 wherein said direction of intersection isperpendicular to said direction of elongation.

5. The tube of claim 4 wherein said aperture in each of said controlelectrode and said screen electrode has an axial ratio ofbetween 1.3 and2.5.

6. An electron gun comprising an electron-emissive cathode, a controlelectrode and a screen electrode, the improvement comprising anelliptical aperture in said control electrode and an elliptical aperturein said screen electrode, said elliptical apertures being coaxial andhaving coplanar major axes.

7. The electron gun of claim 6 wherein each of said apertures has anaxial ratio of between 1.3 and 2.5.

8. In a cathode ray tube comprising an electron-beamresponsive screen,means for projecting a beam of electrons thereagainst, and electron beamaccelerating-focusing apparatus, said means comprising anelectron-emissive cathode, a control electrode and a screen electrode,said tube having a center of deflection for said beam, saidbeam-responsive screen being oriented at an angle acute with respect toa line connecting said deflection center and the center of said screen,the improvement comprising an elongated apcrturein said controlelectrode and an elongated aperture in said screen electrode, the majoraxes of both said apertures lying in a common plane.

9. An electron gun comprising an electron-emissive cathode, a controlelectrode and a screen electrode, the improvement comprising anelongated aperture in said control electrode and an elongated aperturein said screen electrode, said elongated apertures being coaxial andhaving coplanar major axes.

1. In a cathode-ray tube comprising an electron-beam-responsive screen,means for projecting a beam of electrons thereagainst, and electron beamaccelerating-focusing apparatus, said means comprising anelectron-emissive cathode, a control electrode and a screen electrode,said tube having a center of deflection for said beam, saidbeam-responsive screen being oriented at an angle acute with respect toa line connecting said deflection center and the center of said screen,the improvement comprising an elliptical aperture in said controlelectrode and an elliptical aperture in said screen electrode, the majoraxes of both said apertures lying in a common plane.
 2. The tube ofclaim 1 wherein said apertures are coaxial.
 3. The tube of claim 2wherein said apertures are oriented so that said common plane intersectssaid screen in a direction transverse to the direction in which a spotwould be elongated if produced on said screen by a beam of circularcross section projected along said line.
 4. The tube of claim 3 whereinsaid direction of intersection is perpendicular to said direction ofelongation.
 5. The tube of claim 4 wherein said aperture in each of saidcontrol electrode and said screen electrode has an axial ratio ofbetween 1.3 and 2.5.
 6. An electron gun comprising an electron-emissivecathode, a control electrode and a screen electrode, the improvementcomprising an elliptical aperture in said control electrode and anelliptical aperture in said screen electrode, said elliptical aperturesbeing coaxial and having coplanar major axes.
 7. The electron gun ofclaim 6 wherein each of said apertures has an axial ratio of between 1.3and 2.5.
 8. In a cathode ray tube comprising an electron-beam-responsivescreen, means for projecting a beam of electrons thereagainst, andelectron beam accelerating-focusing apparatus, said means comprising anelectron-emissive cathode, a control electrode and a screen electrode,said tube having a center of deflection for said beam, saidbeam-responsive screen being oriented at an angle acute with respect toa line connecting said deflection center and the center of said screen,the improvement comprising an elongated aperture in said controlelectrode and an elongaTed aperture in said screen electrode, the majoraxes of both said apertures lying in a common plane.
 9. An electron guncomprising an electron-emissive cathode, a control electrode and ascreen electrode, the improvement comprising an elongated aperture insaid control electrode and an elongated aperture in said screenelectrode, said elongated apertures being coaxial and having coplanarmajor axes.